Living on Other Planets

I want to speak this evening about living on other planets. I shall begin with an imaginary prediction of the destruction of the Earth, and ask how we ought to take such a prediction. Then we shall consider the possibility of travelling through space, and look in turn at Mercury, Venus, Mars, and the other planets. Finally we shall ask whether there may already be native life on Venus or Mars, or even, strange though it sounds, upon Jupiter and Saturn, or in the Sun itself.

There is one point which ought to be made at the outset. The Earth today is a disunited world. Its peoples are still largely absorbed in war and trade. But the task which I am going to imagine could not be undertaken by a collection of rival nations. All the resources of one whole world would be needed. If mankind were ever seriously to attempt to establish itself on another planet, it must unite.

Let us suppose, then, that one morning there appeared in the newspapers a startling heading: the destruction of the Earth predicted three hundred years hence. The cause might be a collision with some wandering body. Or perhaps the Earth itself was to burst. Or the Moon might somehow fall upon us. None of these events is at all likely, so far as we know; but the supposition provides a useful exercise for the imagination.

How would mankind take the news? At first everyone would be thrilled. But three hundred years is a very long time to ordinary human feeling. The catastrophe would seem too remote to be taken seriously. Some would say, in effect, “Let us eat, drink and be merry.” Only gradually would the reality of the danger sink into the minds of successive generations.

Yet some people would want mankind to continue. They would say, “A great adventure must go on.” Man, after all, is only about a million years old. If the race survived, its possible future might extend for thousands of millions of years. Man might become a far finer being than he is today. Life has advanced from the worm to the monkey and from the monkey to man; perhaps it might advance from man to some kind of superman. Those who felt this possibility vividly would regard it as a sacred duty to preserve mankind.

They would therefore say that we must find another world and send a few men and women to it. Only a few could be sent. The rest must die with the Earth. Gradually this view would become commoner.

How should we set about the task? There would seem to be four main stages. First, we must study the planets by means of telescopes and every other available instrument. Secondly, we must invent what, for convenience, I shall call ether ships—vessels capable of carrying us away from the Earth. Thirdly, we must explore the possible planets and choose the most suitable. Fourthly, we must prepare both the chosen world and mankind itself for the new home.

Travelling in space is not impossible, if we really want to do it. The first vessels would presumably work upon the principle of the rocket to the Moon, though they would have to be huge ships. They might be driven by an explosive mixture; or by subatomic energy.

Once the vessel had passed beyond the atmosphere, it would need no continuous push merely to keep it moving. Power would still be needed for steering and for stopping at the destination. There would also be the danger of meteors, and the danger of incandescence.

The travellers would have to carry their own air. They might take compressed oxygen in liquid form. Food and water would also be required, though these problems are not in themselves so serious. The voyage might last for months or even years, and the ship would therefore need machinery for heating and cooling.

We must not imagine that such a vessel would be perfected at the first attempt. There would have to be many experiments, and almost certainly many tragic failures. A ship might break. It might lose its air, suffer a collision, or fail to return. There might be failures from cold and from heat. The steering apparatus might fail.

Let us imagine the first successful ether voyage. Would the start come with a bump? Perhaps it would. Presently the familiar horizon would begin to contract, rather as it does when seen from an aeroplane. The Earth would reveal its curvature. According to the direction of the sunlight, it would appear circular, gibbous, or crescent-shaped.

As the vessel climbed and the air became thinner, the sky would darken. The stars would become visible even in the presence of the Sun. The Earth would steadily shrink behind the travellers, and terrestrial gravity would weaken. Inside the ship there might have to be some form of artificial gravity—magnetic boots, perhaps, to hold the passengers to the floor.

The first journey would probably be only a trial trip—an approach to the Moon. The travellers might merely circumnavigate it and return. Or they might land, though they could not safely go outside the ship, since there is no air to breathe.

As a new home for mankind the Moon is useless, save as a source of metals and minerals. It has no breathable atmosphere and no water. Its surface is all rock and mountains.

Why has the Moon lost its air? The molecules of a gas are continually darting about at high speeds. In the outermost layers of an atmosphere some molecules move so rapidly that the gravity of a small world cannot retain them. They escape into space, rather as gas escapes with the fizz from soda water when the pressure is released. The Earth is massive enough to retain an atmosphere. The Moon is not. No very small world is possible as a permanent human habitation.

Could we give the Moon an atmosphere? We might imagine transhipping air from the Earth, but the undertaking seems hopeless. Even if we could provide enough, the Moon would not retain it. It would continually trickle away into space, and would be lost in a few thousand years.

Let us now survey the planets according to present knowledge. I must stress that our knowledge is very incomplete. The new two-hundred-inch telescope, when it is brought into use, may tell us much more.

Mercury appears to be useless. It is too small to retain an atmosphere, and it seems, like the Moon in relation to the Earth, to keep one face perpetually turned towards the Sun. On the sunward side the heat would be so great that lead would melt. On the dark side there would be extreme frost, though conditions near the boundary between the two regions might be less violent. An ether ship would melt en route. Perhaps it could be refrigerated sufficiently for a brief exploration, but Mercury offers no reasonable refuge for mankind.

Venus is much more promising, for it is roughly as large as the Earth and has an atmosphere covered by dense cloud. But there is no free oxygen for us to breathe, and in its present condition Venus is therefore useless to mankind. The journey towards it would be very hot. The ether ship would sink through the cloud into a hot, bright mist. What would lie beneath? We do not know. There might be a planetary ocean, or seas and islands, or perhaps some other kind of surface altogether.

If Venus were chosen, it would have to be prepared. First there must be a thorough exploration with settlement in view. Secondly, electrolysis stations might be established to split water and release oxygen. Thirdly, plants would have to be brought from the Earth, probably varieties specially bred for the conditions of Venus. Fourthly, human beings would have to be acclimatised to the heat, to X-rays and other unfamiliar influences. Only after all this could colonisation begin.

And yet colonisation would mean that most men and women on Earth were left behind to die.

There would also be the food problem. At the outset there would be no terrestrial food on Venus. The colonists might have to wait for the imported vegetation to spread, and perhaps there would not be enough time. On the other hand, above the clouds there would be a wealth of sunlight, and this energy might perhaps be used in the production of synthetic food.

In due course generations would be born on Venus. What sort of society would they make? Would they merely reproduce our class wars and national wars under a new sky, or would the transplantation give mankind the opportunity for a new start?

Why should Venus have no free oxygen? Oxygen combines very readily with other elements; one might almost say that it is too friendly. Left to itself, it enters into compounds, and therefore we should not ordinarily expect to find much of it free in an atmosphere. Why, then, is there free oxygen on Earth? Because plants are continually pouring it into the air faster than it can combine with other substances or be breathed by animals.

We might therefore infer that there are no plants of the terrestrial sort on Venus, and consequently no animals dependent upon them. It is a dead world. We may then ask why life did not begin there as it began here. But possibly there is some quite other kind of life which does not require free oxygen. We must not assume that all living things throughout the universe must be built precisely upon the terrestrial plan.

Human settlers would nevertheless have to produce oxygen, either by splitting water through electrolysis, or by introducing plants, or by both methods. Much would depend upon the climate. Is the surface all ocean? Are there islands? Are there storms because Venus lies so near the Sun? In electrolysis the liberated hydrogen might be allowed to escape from the planet, though some might return, and there would be dangers of explosion. The sky beneath the cloud might be bright white. And always there remains the question: might there be native life?

The presence of free oxygen elsewhere would itself be important evidence. Since on Earth it is continually renewed by plants, we may say: free oxygen is present; therefore vegetation exists.

Mars is much smaller than the Earth. It has an atmosphere, but not much of one. At the surface the pressure is lower than that on the summit of Everest. There is oxygen, but only about fifteen per cent of the amount available to us in our own atmosphere. There is also water vapour, but very little. Mars is farther from the Sun and is exceedingly cold. Even at the equator at noon the best one might expect is something like a cold, bright day. In the Martian winter the temperature would be lower than in our Arctic regions.

We could not live there in the open. Perhaps, however, human beings could gradually be acclimatised, and the process might have to begin with babies. The first practical policy would be to establish a sealed ether-ship station or anchorage, and from this protected base gradually to produce a population capable of living more freely upon the planet.

What would the explorers find? Most of the surface would probably be desert—reddish sand or rock. But there are probably large districts covered with something analogous to vegetation, perhaps of a feathery kind. Such regions seem to become greenish in the spring and brown in the winter. There are also the seasonal polar caps and smaller patches, possibly of carbon dioxide. The southern cap vanishes in its summer.

Could Mars support much life? There would be a shortage of water and a shortage of air. There might also be shortages of some of the chemical materials required by living processes. Above all, there is a shortage of light and available solar energy. These shortages would limit how much life Mars could support.

Then there are the so-called canals of Mars—the rather straight-looking lines which seem to run out from the greener regions. Lowell suggested that they might have been made by intelligent beings in order to irrigate the desert. But the whole matter is very doubtful.

Still, if intelligent beings did exist there, the explorers might be resisted. There might be war. We have no idea what Martians would be like. They might be very different from ourselves—as different, perhaps, as the Martians imagined by Wells in The War of the Worlds. The human expedition might simply be destroyed.

Even apart from resistance, many problems would remain. There is first the food problem, made worse by the lack of strong sunlight. Could men eat the Martian vegetables, if there are such things? They might poison us. Could we cultivate terrestrial vegetables? Under the cold, dry conditions and the feeble light, it might be exceedingly difficult.

Would there be coal and oil? Perhaps the colonists would have to burn Martian vegetation directly, supposing it existed in sufficient quantity. There would be no water power and no wind power. There are no great seas to navigate. There is the food problem again, and the shortage of light.

Some ordinary activities would be curiously altered upon Mars. Flying would be difficult in one way because the air is too thin to support an ordinary aeroplane. It would be easy in another way because gravity is slight. Athletics would be easy. A man might jump like a grasshopper.

The asteroids are much too small. They range, roughly speaking, from bodies perhaps ten miles across to bodies some five hundred miles across. On the smaller ones a sufficiently vigorous jump might carry a man off altogether. They have no atmosphere and are extremely cold, and so they cannot be regarded as possible homes.

Jupiter presents the opposite difficulty. It is enormously large and has very powerful gravity. Under such gravity we could hardly stand up. If there are natives, one might expect them to be small and sluggish. Jupiter has a vast atmosphere and perpetual cloud. Whether it has oxygen is another question. It is also very cold, and from it the Sun would appear diminished almost to a mere star.

Saturn would be worse as a home, though it has its ring display and its moons. Uranus is still farther out. From Neptune the Sun would look like a bright arc lamp. Beyond Neptune lies Pluto, colder and more remote still.

What, then, is the upshot of it all? I should say that we might conceivably colonise Venus or Mars, but only with very different types of beings. Anyhow, even if colonisation proves impossible, we may explore those worlds some day.

There have been two opposed old views about life in the universe. According to one, life is possible only here, and the Earth is unique. According to the other, the universe is teeming with inhabited worlds. But in fact planets are rare. The stars themselves are unimaginably numerous: one illustration is that they may be compared with grains of sand sufficient to cover the British Isles to a depth of fifteen feet. Yet if a planetary system is born only once in some two hundred thousand years, there might be only a million or so planetary systems, and only a few of their worlds might be suited to life.

But perhaps we are too ready to identify life with planetary life. J. B. S. Haldane has invited speculation about stellar life. Could there be life in the interiors of stars—in the suns themselves? Could a star be in some sense a fiery brain? Or could there be beings like the salamanders of legend?

The speculation may be extended. Could anything that deserves to be called life occur in nebulae? Could the cosmos as a whole have some living or mental character?

Let me finally gather the argument together and ask what significance this subject has. The imaginary prediction of the Earth’s destruction would have psychological effects upon mankind. It would also reveal the scale of the problems of colonisation.

The ether ship would presumably use the rocket principle, perhaps using subatomic energy. It would have to carry air, food and water, and to provide both heating and cooling. It might need artificial gravitation. Its first soaring from the Earth would expose it to the danger of meteors.

The Moon has no atmosphere because its gravity cannot retain the rapidly moving molecules of gas—the soda-water-fizz principle, as we may rather crudely call it. Mercury likewise has no atmosphere and presents a hot side and a cold side, with temperatures upon the hot side sufficient to melt lead.

Venus is approximately the size of the Earth and is hidden by cloud, but has no known free oxygen, and therefore probably no plants of the terrestrial kind. The explorer would sink through the cloud into a hot, bright mist, wondering whether an ocean, a wholly water-covered surface, or scattered islands lay below, and whether tremendous storms were raging there. Native life might exist; and if it were intelligent, it might attack the newcomers.

To make Venus habitable we should have to introduce plants and release oxygen by electrolysis. We should also have to acclimatise human beings, probably beginning with babies. If these things could be done, Venus might ultimately prove a comparatively wealthy world.

Mars has only about fifteen per cent of our supply of oxygen and very little water vapour. It is a cold, bright, desert world, with seasonal polar caps, perhaps partly of carbon dioxide, and with regions that may be covered by feathery vegetation. There too acclimatisation might have to begin with babies. There too the explorers might be attacked by natives, if the doubtful Martian markings or “clouds” concealed intelligent activity.

Economically Mars would be poverty-stricken. It would have no water power, no wind power and no coal power. On the other hand, the slight gravity would make athletics extraordinarily easy.

The asteroids are too small. On Jupiter we could hardly stand up, and we do not know whether usable oxygen exists there. Any natives must be minute. There too the shortage of light would be serious. Saturn and the farther planets would be worse—the lost tribe, one might say. There is also the problem of planetary formation.

We are therefore brought back to the prerequisites of life. There must be a suitable range of temperature. There must be some flow of available energy; life cannot continue in a state of complete equilibrium. And there must be sufficient diversity of circumstances and materials for complex organisation to arise.

But we ought not to define these prerequisites too narrowly from our own case. There may conceivably be fiery organisms—salamanders, so to speak—where terrestrial life would be burned away.

The final sheet is a compliments slip from the Honorary Treasurers, Martins Bank Limited, 7 Water Street, Liverpool, bearing the Liverpool University Library archive stamp STAP. F13/9; it contains no lecture text.